The present invention concerns a turret punching machine. In particular, the invention concerns a sheet metal punching machine comprising a pair of turrets carrying a plurality of punch and die pairs.
As is known, in turret punching machines, the two turrets are rotatable in order to carry a predetermined punch-die pair to a work station, in vertical alignment with a hammer which acts on the punch. Usually, the two turrets are coaxial and of equal diameter, and have a limited number of punch-die pairs. Consequently, if a working cycle requires a greater number of such pairs, the operator must stop the machine after part of the required punching has been done in order to replace the punch-die pairs already used with other punch-die pairs.
It is clear that stopping the machine and the necessity of using labour to replace the punches and dies increase the processing costs. Furthermore, the machines described cannot be utilised during those work shifts, for example, at night or on holidays time, when the availability of labour is scarce.
Turret punching machines have been proposed in which the two turrets are mounted on two offset axes in order to obtain a zone, substantially opposite the work station, where the two turrets are not superimposed. In this case, the punches and dies can be changed over even during the working.
A punching machine is also known from U.S. Pat. No. 5,346,454 in which the upper turret of the punches has a smaller diameter than the lower turret of the dies, so as to obtain a station for the changeover of the punch-die pair where the upper turret does not cover the lower turret. The machine also has a magazine of punch-die pairs, formed from a pair of rotatable discs fixed to each other and carrying the punches and the dies respectively.
The punch-die pair of the changeover station of the turrets is replaced with a pair carried by the discs by means of a pair of simultaneously rotatable arms which rotate by at 180xc2x0 each time. These arms carry a pair of gripper elements at their two ends, for the punches and the dies respectively, which elements are moveable parallel to the axis of the turrets in order to insert the punches and dies in the respective seats.
In an embodiment of this machine, the two discs have complementary diameters to those of the turrets, while the two arms are of fixed length. In another embodiment, the discs are of equal diameter, but the arm for changing over the punches is extensible in order to compensate for the greater distance of the punches on the disc from the axis of rotation of the arm, with respect to those of the turret. Finally, each gripping element is constituted by simple leaf springs carried on the two arms.
This machine has various disadvantages. In particular, it does not enable the automatic changeover of the punches and the dies where the shape of the magazine or the turrets require a different rotation for the two arms, or for the variation in length of both arms. In addition, the magazine is very cumbersome, even for a limited number of punch-die pairs, since they are only located on the two discs. Finally, the gripper element formed from leaf springs is fairly unreliable.
The object of the invention is to produce a turret punching machine which exhibits the maximum simplicity and safety of operation, and which eliminates the disadvantages described above in relation to the known punching machines.
This object is achieved by the turret punching machine according to the invention, which includes a changeover station for the punch and the die, a magazine having a pair of supports for a series of punch-die pairs, selection means for bringing a predetermined punch-die pair to a collection station, and a pair of changeover elements associated with the said supports for replacing the punch-die pair of the said stations, and which is characterised in that each of the said changeover elements is provided with corresponding displacement means operable to move the said changeover elements selectively and/or independently of each other with respect to the said stations.